Method of making electrical condensers



Oct. 10, 1950 R, B, GRAY 2,525,668

METHOD OF MAKING ELECTRICAL CONDENSERS Filed Feb. 5, 1949 9 l I /4 /3 5\.. ///f//f//f/f//y// /////l 7 I 2f 6 aff-:zi l:

1N V EN TOR.

y Patented ct. 10, y1951i) METHOD OF MAKING ELECTRICAL CONDENSERS Robert B. Gray, Erie, Pa., assignor to Erie Resistor Corporation, Erie, Pa., a corporation of Pennsylvania Application February y5, 1949, Serial No. 74,850 15` claims..r `(C1. 117-66) This application is a continuationV in part of my application 592,946, filed May 10, 1945, and

now abandoned. f

Condensers have been made with dielectrics coated or metallized onl opposite faces. Silver coatings on mica or ceramic dielectrics are most commonly used. The capacity is determined by the overlapping area of the metallized surfaces, the thickness of the dielectric, and the dielectric constant. If the coating is subsequently iired, bubbles may form which cause pin holes decreasing the coating area. Due to the variations in these factors it has not been commercially practicable to manufacture condensers to close limits. This invention is intended to decrease the variation in capacity by measuring the capacity between the coatings during application and stopping the coating at the desired capacity. In a preferred form, one of the coating is red on the dielectric and the other coating is progressively applied in the form of an electrically conducting metallic paint. A control or measuring circuit responsive to the capacity between the coatings stops the application at the desired capacity. Whereas prior methods have resulted in variations of i-10%, the present invention can easily reduce the variations to a fraction of 1%, i16% or .1 mmfd. being readily feasible. Further objects and advantages appear in the specication and claims.

In the drawing, Fig. 1 is a sectional View of a tubular ceramiccondenser; Fig. 2 is a diagrammatic view of the apparatus for applying onel of the coatings; Fig. 3 is a sectional view of another form of apparatus for applyingone of the coatings; Fig. 4 is an end View of the apparatus of Fig. 3; and Fig. 5 is a diagrammatic view of another modication of the coating apparatus.

In Fig. 1 is shown a condenser having a ceramic tube I having an inner metal coating 2 and an outer metal coating 3. The coatings are produced by the techniques used in the decoration of ceramics, mica, quartz and glass. The inner metal coating extends over one of the ends of the tube and has a portion 4 on the outer surface of the tube making contact with a spring terminal cap'5 having a lead 6. A similar spring terminal cap l having a lead 8 contacts the outer coating at the other end of the tube. The condenser may be imbedded in insulating material 2 9` indicated by dotted lines. The condenser so far described is of common construction.

The capacity of the condenser is determined by the overlapping (projected) area of the coatings 2 and 3 and by the ywall thickness and dielectric ccnstantof the dielectric. Due to the variation of these factors it has been difcult to maintain close limits on the capacity of the condensers. In the present invention the capacity between the coatings is measured during application and the coating application is stopped when the desired capacity is reached. This permits the capacity of the finished condenser to be more accurately determined.

In the apparatus indicated in Fig. 2, the inner coating 2 is fired on the ceramic tube and a wax plug I0 closes the lower end of the tube. A terminal II is connected to the inner coating at the upper end of the tube to a measuring and control circuit I2. The condenser is then dipped in a paint I3 either by raising the paint container I4 or by lowering the condenser. When the capacity between the inner coating and the paint reaches the desired value, the condenser may be liftedk out of the paint and the condenser fired to'set the outer coating. yVariations in the dielectric constant and wall thickness are automatically compensated by the control of the dip` the accuracyfof measurement of the capacity is unaffected by stray capacities due to the geometrical arrangement of the condenser and paint container. These capacities are constant forany particular coating apparatus. The capacity between the inner and outer coatings before ring will therefore very closely represent the capacity of the finished condenser.

In Figs. 3 and 4 after firing the inner coating 2, the tube is slipped over a terminal I5 carried in an insulating bushing I6 in a holder I'l which maybe mounted in a chuck to slowly rotate the tube. The outer surface of the tube is contacted by a striping Wheel I8 carried by a spindle I9 on an arm 2|. The lower part of the striping wheel dips into a paint container `2!) and prof gressively applies the outer coating. The terminal I 5 andthe striping wheel I8 are respectively connected to the high andK grounded sides vof 3 the measuring circuit l2. When the desired ca- Dacity is reached, a solenoid 22 is energized lifting the arm 2l and moving the striping wheel away from the tube.

In Fig. the outer coating is iired on the ceramic tube and the lower end of the tube is then seated on a table 23 registering with an orifice 24 connected to a pump 26 for pumping paint up into the interior of the tube. The table is connected to an electrode 25 extending up within the tube for lowering the resistance to the inner coating. The outer coating and the electrode 25 are respectively connected to the high and grounded sides of the measuring circuit. When the liquid level reaches the value corresponding to the desired capacity the solenoid 22 is energized and lifts the tube off the table, breaking the seal between the lower end of the tube and the orifice 24 and dropping the liquid level.

The coating procedure may also be used to adjust the capacity of finished condensers to the desired value. In this procedure both the inner and outer coatings are fired on the tube, and the tube is mounted on a spindle similar to that i.

shown in Fig. 3. The operator with a paint brush adds to the outer coating until the capacity between the coatings reaches the desired value. With this arrangement the capacity depends upon the accuracy with which the operator can stop ..1

the added coating at the desired value of capacity. As in the previous constructions, the outer coating, the coating which is being increased in area, will be connected to the grounded side of the measuring circuit so that the body capacity of the operator will not interfere with the accuracy of measurement.

The coating processes require an electrically conducting metallic paint, i. e. a paint having high electrical conductivity prior to drying. Such a paint produces a wet nlm having suiiiciently low resistance to permit accurate measurement of capacity. Such paints have been made with precipitated silver or silver oxide pigments, a lm forming vehicle of ethyl cellulose, polyvinyl alcohol or purified dextrin, and a water or alcohol base. To the paints may be added ceramic fluxes or other bonding agents for increasing the adherence of the coating, antifoaming agents for preventing bubble formation in the coating (decreasing the area of the fired coating), and agents for increasing the hydrogen ion concentration to lower the resistance of the coating. After the base has evaporated, the coating has too high an electrical resistance for accurate measurement of the capacity, so the capacity measurement should be made before the base has evaporated.

The paints, like the paints heretofore used in the decoration of ceramics, mica, quartz and glass, comprise a compatible mixture of a base, a vehicle, and a pigment and flux. The base is a thinner providing the desired consistency for spreading, dipping or spraying. Its function starts with providing the desired consistency and ends when the film is dried. The vehicle functions as a temporary binder or adhesive holding the film in place. Its function starts with the application of the wet film and ends with the firing when the vehicle breaks down. The pigment and flux come into action on ring to produce a metal lm held in place by the flux. Fluxes are well known and the choice of uxes is determined by the firing temperature and the material being coated. Bismuth subnitratagmercuric oxide, lead oxide, lead borate, and lead silicate are common uxes. Although usable with other materials, these fluxes are known as ceramic iiuxes.

The following are the constituents of paints which have been used:

Per cent (l) Precipitated silver (with or without silver chloride, an active impurity) 50 Ceramic ilux 2 to 10 Polyvinyl alcohol 4 Ammonia .2 to 1 Water balance (2) Precipitated silver oxide 50 Ceramic flux 2 to 10 Polyvinyl alcohol 2 Ethyl alcohol 2 to4 Water balance (3) Precipitated silver oxide 50 Ceramic iiux 2 to 10 Purified dextrin 4 Silver nitrate Oto 5 Water balance (4) Finely divided silver 60 Silver nitrate 3 Ceramic llux 2 to 10 10% solution of silver protein in water such as sold under the trade name Argyrol balance (5) recipitated silver oxide 50 Ceramic flux 2 to 10 Polyvinyl alcohol 2 Ethyl alcohol 2 to 4 Silver nitrate 0 to 3 Water balance The pigment in the paint in Example 1 tends to settle so that the paint has to be stirred during application, The paints in Examples 2 and 3 are very stable and can stand for some hours during use without requiring stirring. There is no trace of reaction between the constituents of Example 2 in six months. The silver nitrate in Examples 3y and 5 must be added shortly before use to prevent breakdown of the vehicle. It can have a very low electrical resistance and is therefore adapted to coating by the striping or brushing process where the capacity is high enough to make the series resistance more than a few ercent of the capacitive reactance. With all of the paints the dried coating has too high an electrical resistance for capacity measurements. The conductivity is due to the suspending medium and ions dissolved in it, since the pigments are insulated by the film forming material.

The constituents do not react chemically but form a mixture in which each of the constituents functions substantiallyindependently of the other constituents. The percentage of pigment depends upon the thickness of the coating to be applied. After heating or ring the pigment formsV a uniform silver coating held in place by and alloyed with the ceramic flux. The remaining constituents are broken down during the firing. The amount of ceramic flux necessary depends upon the type of `ceramic or other dielectric. The amount and kind of flux for any particular dielectric is well known. Other bonding agents may be used. The firing or baking temperature is primarily determined by the heat necessary to set the bonding agent. Firing is used to define the necessary setting heat.

The film forming vehicle (or protective colloid) holds the pigment in suspension and upon drying, holds the coatingA againstvthe ceramic surface until the firing operation. The antifoaming 'agent is necessary with some vehicles butnot with others. For example, the purified dextrin requires no antifoaming agent. Each of the constituents acts independently and belongs to a class of materials having `well known properties.

`The constituents are chosen to have no harmful reaction. For example, silver nitrate attacks some vehicles, such as polyvinyl alcohol, but does not attack dextrin within the normal period of use. With polyvinyl alcohol, the silver nitrate should be added immediately prior to use. Chlorides should be avoided as these have a tendency to form silver chloride which is undesirable in the finished coating. These factors are well understood in the art.

Silver oxide, when dry, is explosive. base is therefore desirable from the standpoint of safety.

What I claim as new is:

1. The method of making electrical condensers v which when finished have a dielectric with opposite metallized surfaces which includes progressively applying to one of the surfaces of the dielectric in overlapping relation to the opposite metallized surface of the dielectric an electrically conductive metallic paint of the type reducible by firing to a metallized coating while measuring the capacity between the wet coating and the opposite metallized surface, terminating the application of the progressively applied coating at the desired capacity, and firing the dielectric to set the coating.

2. The method of controlling the capacity of electrical condensers having a dielectric with metallized coatings on opposite surfaces thereof in overlapping relation which comprises applying one of the coatings to progressively overlap the other coating, measuring the capacity between the progressively applied coating and the other coating while the progressively applied coating is wet, and terminating the application at the desired capacity.

3. The method of adjusting the capacityof an electrical condenser having a dielectric with metallized coatings on opposite surfaces thereof in overlapping relation which comprises applying to one of the surfaces a coating of an electrically conductive metallic paint of the type reducible by firing to a metallized coating to increase the area of said one surface overlapping the metallized coating on the opposite surface, measuring the capacity between the surfaces while the progressively applied coating is wet, terminating the application of the paint at the desired capacity, and ring the dielectric to set the paint.

4. The method of making electrical condensers of the type having a dielectric with metallized coatings on opposite surfaces thereof and in overlapping relation which comprises ring one of the coatings, progressively applying the other coating in the form of an electrically conductive paint of the type reducible by firing to a metallized coating, measuring the capacity between the coatings while the progressively applied coating is wet to determine the stopping point in the application of theA paint, and firing the condenser to set the paint.

5. The method of making electrical condensers of the type having a dielectric with metallized coatings on opposite surfaces thereof in overlapping relation which includes applying one of the coatings in progressive overlapping relation to the other coating in the form of an electrically conductive paint of the type reducible by firing A water to a metallizedcoating andhavingan evaporatingelectrically conductive base which prior to evaporation imparts a low resistance to the coating, measuring the capacity between the coatings prior to the evaporation of the base to determine the stopping point in the application of the paint, and firing the condenser to set the paint.

6. The method of making electrical condensers having a dielectric with opposite metallized surfaces in overlapping relation which includes progressively advancing the liquid level of a metallic electrically conductive paint, of the type reducible by firing to a metallized coating, in contact with one of the surfaces and in the direction to increase the overlapping surface area, measuring the capacity to the wet paint, and terminating the advance when the desired capacity is reached, and ring the dielectric.

7. The method of making electrical condensers having a tubular dielectric with an inner metallized surface which includes spirally applying a metallic coating of an electrically conductive paint of the type reducible by firing to a metallized coating to the outer surface, measuring the capacity between the spirally applied coating and the other surface while the spirally applied coating is wet, terminating the application when the desired capacity is reached, and firing the dielectric.

8. The method of making electrical condensers having a tubular dielectric with an outer metallized surface which includes advancing a column of electrically conductive metallic paint of the type reducible by firing to a metallized coating along the inner surface of the tube, measuring the capacity between the column and the outer surface, terminating the advance at the desired capacity, and firing the dielectric.

9. The method of making silver ceramic electrical condensers which comprises firing a silver coating on one surface of a ceramic dielectric, applying a wet film of an electrically conductive silver paint, of the type reducible by firing to a metallized silver coating, to the opposite surface of the ceramic dielectric to progressively overlap the red coating, measuring the capacity between the fired coating and the wet film, terminating the application of the wet` film at the desired capacity, and firing the ceramic to set the wet film.

10. The method of making silver ceramic electrical condensers which comprises firing a silver coating on one surface of a ceramic dielectric, advancing over the opposite surface of the ceramic dielectric to progressively overlap the fired coating an electrically conductive silver paint of the type reducible by firing to a metallized silver coating, measuring the capacity between the fired coating and the wet paint, terminating the advance of the paint at the desired capacity, and ring the ceramic to set the paint on the opposite surface.

1l. The method of making silver ceramic electrical condensers which comprises firing a silver coating on one surface of a ceramic dielectric, applying a wet lm of an electrically conductive silver paint, of the type reducible by firing to a metallized silver coating, to the opposite surface of the ceramic dielectric to progressively overlap the fired coating, grounding the wet film, measuring the capacity between the fired coating and the wet lm, terminating the application of the wet lm at the desired capacity, and firing the ceramic to set the wet lm.

12. The method of making silver ceramic electrical condensers which comprises firing a silver coating on one surface of a ceramic dielectric, advancing over the opposite surface of the ceramic dielectric to progressively overlap the red coating, an electrically conductive silver paint of the type reducible by iiring to a metallized silver coating, grounding the paint, measuring the capacity between the fired coating and the paint, terminating the advance of the wet paint at the desired capacity, and ring the ceramic to set the paint on the opposite surface.

13. The method of making silver ceramic condensers which comprises producing a metallized silver coating on one surface of a ceramic dielectric, applying to the opposite surface of the ceramic dielectric to progressively overlap the metallized coating a silver oxide pigment paint suspended in an electrically conductive base and reducible by ring to a metallized silver coating, grounding the paint, measuring the capacity between the wet paint and the coating, terminating the application of the paint at the desired capacity, and ring the ceramic to reduce the silver oxide to silver.

14. The method of making electrical condensers which when finished comprise a dielectric having metallized coatings on opposite surfaces of the dielectric in overlapping relation to provide the desired capacity between the overlapping portions of the coating which includes the steps of applying an electrically conductive coating progressively to overlap the other coating, measuring the capacity to the progressively applied coating during application and terminating the a metallized coating and in a manner to progressively overlap the other coating, measuring the capacity between the overlapping'coatings during application of the progressively applied coating and prior to evaporation of the base, terminating the application of the progressively applied coating at the desired capacity, and ring the coating.

ROBERT B, GRAY.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,682,457 Zworkin Aug. 28, 1928 1,717,193 Dantsizen June 11, 1929 1,962,438 Flanzer et al June 12, 1934 2,061,106 Schellinger Nov. 17, 1936 2,390,784

Drobisli et al. Dec. 11, 1945 

1. THE METHOD OF MAKING ELECTRICAL CONDENSERS WHICH WHEN FINISHED HAVE A DIELECTRIC WITH OPPOSITE METALLIZED SURFACES WHICH INCLUDES PROGRESSIVELY APPLYING TO ONE OF THE SURFACES OF THE DIELECTRIC IN OVERLAPPING RELATION TO THE OPPOSITE METALLIZED SURFACE OF THE DIELECTRIC AN ELECTRICALLY CONDUCTIVE METALLIC PAINT OF THE TYPE REDUCIBLE BY FIRING TO A METALLIZED COATING WHILE MEASURING 